原来UIScrollView自带了一个下拉刷新的控件。但是并不是那么好用，于是做了一些封装。

UIRefreshControl:

发现UIRefreshControl 很简洁，

1. refreshing 一个状态属性
2. tintColor 一个菊花圈圈的颜色
3. attributedTitle 一个刷新时显示的文字
4. -(void) beginRefreshing 开始刷新, 根据偏移量 会自动进入刷新。
5. -(void) endRefreshing 结束刷新，必须自己调用

不难发现这边少了一个开始刷新的回调。简单一点的我们可以这么做:

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{
    if (self.refresh.isRefreshing) {
        NSLog(@"开始刷新了😝");
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3*NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [self.refresh endRefreshing];
        });
    }
    NSLog(@"y = %f , x = %f", scrollView.contentOffset.y, scrollView.contentOffset.x);
}

但是每次都去写一个代理，看起来并不是那么友好啊。所以有了下面的事情:

#import "UIScrollView+LJRefresh.h"
#import <objc/runtime.h>

@interface UIScrollView ()

@property(nonatomic, strong)void(^refreshHandler)();

@end

@implementation UIScrollView (LJRefresh)

+(void)load{
    Method originalMethod = class_getInstanceMethod([self class], NSSelectorFromString(@"handlePan:"));
    Method swizzledMethod = class_getInstanceMethod([self class], @selector(customPanGesture:));
    method_exchangeImplementations(originalMethod, swizzledMethod);
}

static char refreshBlockKey;
-(void (^)())refreshHandler{
    return objc_getAssociatedObject(self, &refreshBlockKey);
}

-(void)setRefreshHandler:(void (^)())refreshHandler{
    objc_setAssociatedObject(self, &refreshBlockKey, refreshHandler, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

-(void)addSystemHeadRefresh:(NSString *)title handler:(void (^)())handler{
    
    UIRefreshControl* refresh = [[UIRefreshControl alloc]init];
    NSAttributedString* attributeStr = [[NSAttributedString alloc]initWithString:title];
    refresh.attributedTitle = attributeStr;
    refresh.tintColor = [UIColor redColor];
    self.refreshControl = refresh;
    self.refreshHandler = handler;
}

-(void)customPanGesture:(UIPanGestureRecognizer *)gestureRecognizer{
    if (gestureRecognizer.state == UIGestureRecognizerStateEnded) {
        if (self.refreshControl.isRefreshing && self.refreshHandler) {
            self.refreshHandler();
        }
    }
    [self customPanGesture:gestureRecognizer];
}

-(void)beginSystemHeadRefresh{
    [self.refreshControl beginRefreshing];
}

-(void)endSystemHeadRefresh{
    [self.refreshControl endRefreshing];
}
@end

没错，就是写个UIScrollView的分类，再把ScrollView上面原来的Pan手势的Action 用黑魔法转换，再监听手势结束后的状态。就是我们需要的开始刷新状态了。
使用的时候 就这么着:

@weakify(self);
[self.contentScrollView addSystemHeadRefresh:@"😁😎😆hello" handler:^{
     @strongify(self);
     DLog(@" 开始刷新啦`````");
     dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.35*NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
          [self.contentScrollView endSystemHeadRefresh];
     });
 }];

refresh.gif

附上Git地址 https://github.com/DistanceLe/AllTools